A scalable electrothermal large-signal AlGaN/GaN HEMTs model for both fundamental and multiharmonics is presented based on the modified Angelov model. To obtain accurate scalability of the electrothermal model, a simple empirical expression is proposed for the geometric and power-dissipation-dependent nonlinear thermal resistance R _th . Only one additional parameter with linear scaling rule is needed in the drain-source current (I _ds ) model for a scalable large-signal multiharmonic model. The proposed model has been validated by different AlGaN/GaN HEMTs characterized by on-wafer measurements. It shows that the presented scalable model can well predict the dc I-V, pulsed I-V, scattering (S) parameters, and large-signal performance up to third harmonic. Furthermore, to further validation, a C-band power amplifier is designed. The amplifier is realized using the second-harmonic tuned approach to enhance the efficiency. Measurement results show that the GaN high power amplifier (HPA) microwave monolithic integrated circuit (MMIC) exhibits more than 40% power-added efficiency and 60-W output power (P _out ) with associated gain of 25 dB in 5-6 GHz measured at 28-V drain voltage and pulse signal with 100-μs pulsewidth and 10% duty cycle. The area of the chip is 3.2 mm × 5.3 mm (16.96 mm ² ). These results show that the proposed model will be useful for high-efficiency HPA MMIC design.

This paper presents an accurate quasi-physical compact large-signal model for GaN high electron mobility transistors (HEMTs). The drain current $I_{\mathrm {ds}}$ expression is acquired by combining the zone division method and the surface potential theory. The proposed $I_{\mathrm {ds}}$ model only contains 19 empirical parameters, with self-heating, ambient temperature and trapping effects considered. The self-heating effects are modeled by a polynomial function of temperature and gate voltage for the critical electric field $E_{c}$ . And the ambient temperature effects are modeled by modifying pinchoff voltage and maximal electron saturated velocity. The trapping effects are considered with an effective gate–source voltage method. Moreover, taking the advantage of good physical meaning, the proposed $I_{\mathrm {ds}}$ model is scalable. In house 0.15- $\mu \text{m}$ GaN HEMTs with different sizes are used to validate the model by dc $I$ – $V$ over a wide ambient temperature range, pulsed $I$ – $V$ , multibias S-parameters up to 50 GHz and multibias large-signal characteristics at $f_{0} = 30$ GHz. The good results show that the proposed quasi-physical zone division model is useful for millimeter-wave GaN HEMTs development and circuit design.

This paper presents a universal scalable thermal resistance model for AlGaN/GaN high electron-mobility transistors (HEMTs), which can be easily implemented into compact large-signal models and is very suitable for rapid device modeling. It contains all the key HEMT device geometric parameters such as gate length, gate width, gate pitch, and different layer thicknesses. The temperature-dependent conductivities of different materials are taken into consideration. The via-holes effects on the thermal resistance of a device are also included, which is considered for the first time in a compact large-signal model. Two uniform parameters are used to simplify the complicated analytical closed-form expression of thermal resistance, which is difficult to be implemented into the compact model. Another two uniform parameters are used to simplify the complicated transcendental function of the temperature rise with respect to the temperature-dependent thermal conductivity. Thus a simple, accurate, and scalable thermal resistance model can be obtained. The results are verified by comparing with experimental and finite-element numerical simulations. The dc I-V characteristics and large-signal performances of HEMTs devices with different gate lengths 0.15, 0.25, and 0.4 μm are used for further verifications. The proposed thermal resistance model can also be used to optimize the structural geometry of a device to obtain minimum thermal resistance.

In this paper, a new method for the separate extraction of the temperature-dependent source (R _s ) and drain (R _d ) access resistances in gallium nitride (GaN) high electron-mobility transistors (HEMTs) by using the definition of access resistances is reported. Based on this method, the temperature-dependent access resistances (TDARs) of a 0.15 μm gate-length GaN HEMT with unequal gate-source and gate-drain distance are extracted. By integrating the extracted access resistances into a modified Angelov model, the effects of TDARs on millimeter-wave (mmW) large-signal performance of the 0.15 μm GaN HEMT at different ambient temperatures (i.e., -55 °C, 25 °C, and 85 °C) are investigated. Moreover, the influence of temperature coefficient difference between R _s and R _d due to the asymmetry of the device has been also revealed. The results show that the TDARs have large impact on the large-signal modeling of mmW GaN HEMTs, and the temperature coefficients of R _s and R _d need to be considered separately in the modeling of asymmetric GaN HEMTs. The proposed TDARs extraction method would be useful for accurate modeling of GaN HEMTs at mmW frequencies.

In this paper, the buffer-related current collapse (CC) in AlGaN/GaN HEMTs is investigated by using pulsed I-V measurements and 2-D drift-diffusion simulations. The simulation results indicate that the negative potential (NP), appearing in the Fe-doped buffer under the gate, is found to account for the CC. The NP will induce threshold voltage shifts, in which an inflection point (IP) of the threshold voltage is found. It could be revealed in pulsed I-V characteristics which are significant to depict trapping effect when building a compact large-signal model. The formation mechanism of the IP is detailed. In the end, a simple threshold voltage model is proposed for verification.